28 S-MITHSONIAX MISCELLANKOUS COLLECTIONS VOL. 53 



pleural lobes four anchylosed segments are outlined by narrow, 

 deep furrows ; only the two anterior preserve any trace of the pleural 

 furrow, and these are very short and obscure ; the pleural segments 

 are mainh- made up of the thickened, broad, anterior border and 

 the strong, backward-extending, rounded spines ; the outer border 

 is usually obscured until after the fourth spine is passed, and even 

 then in some specimens the short fifth and sixth pairs of spines 

 obscure it ; on other specimens the posterior spines are so slightly 

 developed that the outline of the border ;s preserved. 



Surface finely granular. 



Dimensions. — A dorsal shield 38 mm. in length has the follow- 

 ing dimensions : 



Cephalon : mm. 



Length 13.0 



Width at base 30 . 



Length of eye lobe 7.0 



Length of glabella 10 . C 



Width of glabella, base 6.0 



Width of glabella, front 6.5 



Thorax : 



Length 17.5 



Width 21.0 



Axial lobe, anterior segment 8.0 



Axial lobe, posterior segment 4.5 



Pleural lobe, anterior segment 6.5 



Pleural lobe, posterior segment 3.0 



Pygidium : 



Length 7.5 



Width 10. o 



Axial lobe, anterior segment 4.5 



Axial lobe, posterior segment 2.5 



The preceding description is based on adult specimens averaging 

 38 to 45 mm. in length. A large number of young and small speci- 

 mens were found in association with the larger adults, some of 

 which exhibit stages of growth. A specimen 1.9 mm. in length 

 (fig. 5) preserves the cranidium and five segments of the thorax. 

 The glabella widens out toward the front, and the occipital furrow 

 is very faint ; the base of the palpebral lobe is farther out on the 

 posterior margin than in the adult, and its anterior end is at the 

 dorsal furrow and nearer the antero-lateral, rounded angle of the 

 glabella. The pleural lobe has somewhat broader, more direct fur- 

 rows on the pleura, and the spine of the fifth segment is very large ; 

 another important character is the greater extension of the terminal 

 spines of the third thoracic segment — a character unknown in the 



